淮海工学院毕业设计翻译Word文档格式.docx

淮海工学院毕业设计翻译Word文档格式.docx

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MrDanielJohnClarke

infulfilmentoftherequirementsof

CoursesENG4111andENG4112ResearchProject

towardsthedegreeof

BachelorofEngineering（Mechanical）

Submitted:

November,2006

6.5ParallelogramMechanism........................................................................................46

6.6SpringDesign...........................................................................................................49

6.7Designofcastorframe.............................................................................................54

6.8Hubdesignandwheelselection...............................................................................56

6.9Spoolvalvecontrol...................................................................................................60

6.10Spoolvalveselection...............................................................................................63

ABSTRACT

Thepurposeofthisprojectwastodesignaheightcontrolsystemthatcouldbeappliedto

aThreePointLinkagemountedimplement.Severalmethodsofachievingthisgoalwereinvestigated.Thetwomethodsthatwereinvestigatedindetailwereanelectricaloverhydraulicsystemandamechanicaloverhydraulicsystem.

Theuniqueoperationofthethreepointlinkageimplementswhenliftassistisusedpresentsproblemswhenaccurateframeheightisrequired,suchaswhenseedingoperationsarebeingperformed.Thesystemhasbeendesignedsothatitisconstantlysensingtheheightoftheframeatbothendsoftheimplement.Theoutputfromthissensingisusedtocontrolahydraulicvalvemechanicallyorelectrically.Ifaheightdiscrepancybetweenthefrontandrearoftheimplementisdetected,thisvalvewillbe

activatedtoallowaflowofhydraulicoiltotheliftassistsystem,levellingtheimplement.

Theinvestigationoftheelectricalcontrolsysteminvolvedconstructingaprototype

circuitthatwasbasedonaPICAXEmicrocontrollertoprovidecomputingpower.This

chipwasprogrammedtoreadtheoutputfromtwovariableresistorsanddetectanyheightdiscrepancies.Whenadiscrepancywasdetected,themicrocontrolleractivatedaservomechanismthatusedmechanicalmotiontocorrectthepositionofoneoftheresistor

tomatchthemechanicalpositionofthetworesistors,thusprovingtheconceptofmechanicalheightcontrol.

Themechanicalsystemwasdesignedsothattheoutputfromtwoheightsensingwheelswasmechanicallyinputintothehydraulicvalvetoactuateitwhenthewheelssensedthat

therewasaheightdiscrepancy.Thissystemwasmodelledusingthesolidmodelling

packageSolidWorksandbasicengineeringanalysiswasperformedonthedesign.

FacultyofEngineeringandSurveying

ENG4111ResearchProjectPart1&

ENG4112ResearchProjectPart2

6.5ParallelogramMechanism

Figure6.5:

Imageshowingthefinalparallelogramdesign

Theparallelogrammechanismwasbuilttocombinemanyfunctionsinthesameunit.

Figure6.5showsanimageofthesolidmodelofthemechanism.Backingplate（A）actsas

aninterfacebetweenthemechanismandtheimplementframe.ThisissecuredtotheframewiththeU-bolts（B）.Notethattherearefourdifferentheightsettingsthatareavailable

fromthetwelveholesinthebackingplate.Thisallowstheheightsensingmechanismtobe

adaptedtosuittheheightofmostimplements.Theframeintheimageismadeofsimple4”

squarerolledhollowsection（RHS）,althoughadapterblockswillbesuppliedwiththedevicetofittheseU-boltstoavarietyofdifferentframesizes.Theheightsettingshown

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showsthecorrectsettingtosuita（lowered）frameheightof800mm,asmaybefoundon

largetrailingimplements.Thelargeheighttravelrangeofthemechanismcoupledwiththefourheightsettingsensuresthatthisdevicecanbefittedtomostthreepointlinkageandtrailingimplementsifthisisnecessary.

Thelowerlink（D）andupperlink（E）aremadeof50x63mmRHSwitha3mmwall

thickness.Notethatthesedimensionscorrespondto2x2½

”,whichisacommonRHSsize.Botharefittedateachendwithgreasablebearingtubesasdescribedpreviouslythatareweldedontothewallsofthesection.Fourofthesemakeupthepivotingpointsforthemechanism.Theupperandlowerlinksarebothfittedwith20mmshafts（FandG）thatprotrudefromthelinksandprovidemountingpointsfortheshockabsorber（I）andspringmechanism.ItemCformsthefourthsegmentoftheparallelogram,andisthepartthat

holdsthecastorframewhichinturnholdsthewheel.Thecastorpivot（H）ismadeofanothergreasablebearingtubethatissizedtofita30mmshaft.Fulldetailofallofthesepartsarcanbefoundintheappendices.

Theshockabsorberisfittedtotheframetodampexcessmotionresultingfromrough

terrain.Ifthiswasnotdone,therewouldbealmostconstantactivationofthespoolvalveineventhesmoothestterrain,resultinginerraticheightcontrolandexcesswearofthespoolvalveandlinkages.Theshockabsorberspecifiedforthisapplicationisaunitfromtherear

ofaNissanPatrolFourwheeldrive,partnumberIA30.Thisunitwasdesignedforaheavyvehicle,sooffersahighamountofenergyabsorptioncapacity,aswellasalonglifeandreliability.Thestrokeofthisunitismeasuredat230mm,whichifthegeometryissetcorrectlyisenoughforthisapplication.

Thegeometryofthefinaldesignofthemechanismmeansthatthegreatestdampingforceoccursattheworkingheightwhereitismostneeded,andalmostnodampingforceispresentwhentheframeisfullyextendedanddampingisnotascritical.Thismethodof

designmeansthatthedampingforcecanbeadjustedbychangingtheheightsettingofthe

U-boltsthatsecurethebackingplatetotheframe.Usingtheupperboltholeswillincrease

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thedampingforcebyraisingthewheel,whereasusingthelowerboltholeswillreducethe

dampingforcebyeffectivelyloweringthewheel.

Aviewoftheothersideofthemodelisshowninfigure6.6.Thisshowsthemechanismthatmountsaspringtothemechanism.Thisspringisnecessarytoprovideforcetopushthewheeldowntoprovideanaccuratecontourfollowingability.Theotherjobthatthe

springmustperformistoforcethewheeltotraveldownwardsfastenoughsothateveninarapidliftingphase,thewheelremainsincontactwiththeground.Thismeansthatthe

springmusthaveenoughforcetoextendtheshockabsorberatthecorrectspeedtokeepthewheeltouchingtheground.

Figure6.6:

Secondaryimageofthefinalparallelogramdesign

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Thespringholderworksbyprovidingtwoplates（FandE）thatpressoneitherendofthe

springandcontainit.These

platesmoverelativetoeachotherastheframemoves

vertically,keepingthespringcompressedandprovidingdownwardforcetothewheel.TheplatesarealignedwithashaftBthatisconnectedtobossassemblyGandslidesrelativetoalignmentbossA.Theslidingshaftisalsolocatedcoaxiallyinsidethecoilsofthespring,thereforecontainingitbetweenthetwoplates.Thealignmentbossisheldontheupper

20mmshaftbyasplitpinandawasher（D）insteadofacollarandbolt（C）.Thisisbecausetheslidingshaftistooclosetothepivotshafttoallowacollarandbolttobeused.

6.6SpringDesign

Asthespringholderandtheshockabsorbersharethesamemountingpointstopand

bottom,theextensionforceontheshockabsorberduringliftingoftheimplementisequal

tothecompressionforcefromthespringminustheforcethatthespringisexertingonthegroundthroughthetyre.Thefastertheliftingaction,themoreofthespring’sforceisgoingintoextendingtheshockabsorber.Thereforethespringshouldbeabletoexertenough

forcetoextendtheshockabsorberatafastenoughratetokeepupwitharapidliftandprovideenoughadditionalforcetokeepthetyreincontactwiththegroundatthesametime.

Theshockabsorberunitthatwasobtainedformodellingpurposeswaswornout,sothecompressiondampingforcethatwasmeasuredwasnotrepresentativeofanewunit.Theextensiondampingforcefeltalotstrongerhowever,andwasenoughtoprovidearough

guidetotheexpansiondampingfactorofanewunit.Thisisthecriticaldampingfactorthatwouldgovernthedesignofthespring.Togetafeelforthedampingfactor,anextension

forceofanestimated20kgwasappliedtotheshockabsorberbyhandandtheextension

ratewasestimated.Thetestingprocedurewasonlyanapproximationbecauseasmentionedpreviouslythetestunitwaswornoutandcouldonlyprovidearoughguideanyway.

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Thistestindicatedthataforceof20kgwouldresultinanextensionspeedofapproximately

20mm/second.Itisestimatedbyvisualobservationthatthemaximumexpectedliftrateof

athreepointlinkageimplementisapproximately100mm/second.Notethatthisdeviceisnotbeingcustomisedtofitonetractor;

itisdesignedtobeuniversallyusedonawide

varietyoftractor/implementcombinations.Thustheaimofthisdesignprocessistocome

upwithamaximumfeasibleliftratefigurethatcouldbeencounteredanddesignaspring

thatwillbeabletoextendtheshockabsorberatthecorrectrateandatthesametimesupplysufficientforcetopressthetyreintotheground.Thusbasedontheobservationsoftheoperationofthreepointlinkagesystems,itisdecidedtodesignthespringtolowerthe

wheelatarateof200mm/s.Thisspeedis